Effects of specific interactions

Some bichromophoric systems, whose structure is based on the donor-bridge-acceptor principle, can undergo complete charge transfer, i.e. electron transfer. The resulting huge dipole moment in the excited state explains the very high sensitivity to solvent polarity of such molecules. An example is FP (l-phenyl-4-[(4-cyano-l-  

The dipole moment in the excited state was estimated (by means of Eqs 7.8 and 7.9) to be 31.8 D. The fluorescence maximum is located at 407 nm in n-hexane and 697 nm in acetonitrile. Unfortunately, protic solvents cause complete quenching therefore, this family of molecules cannot be used as polarity probes in protic microenvironments. 

Several examples described above have shown that specific interactions such as hydrogen bonding interactions should be considered as one of the various aspects of polarity. This important point deserves further discussion because hydrogen bonding can lead in some cases to dramatic changes in absorption or fluorescence spectra. 

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A very marked effect of specific interactions can also be observed with anthroyl derivatives and in particular with methyl 8-(2-anthroyl)-octanoate. The fluorescence spectrum of this compound in hexane exhibits a clear vibrational structure, whereas in N,N-dimethylformamide and ethanol, the loss of vibrational structure is accompanied by a pronounced red-shift (Figure 7.6) (Perochon et al., 1991). 

The approach of specific interactions, developed primarily by Pitzer (1973) and Whitfield (1975a,b), considers all salts, from a purely formal point of view, as completely dissociated, and embodies the effects of specific interactions into particular activity coefficients, defined as total activity coefficients or stoichiometric activity coefficients, with symbol y. For instance, for ion /,... 

The Effect of Specific Interaction on Cloud Point Curve.152... 

The Effect of Specific Interactions on Cloud Point Curves... 

One would expect the organic phase of other amine extraction systems in which more than one metal anion can be formed to exhibit similar equilibria. It is fortunate that in this system not only is the solvent not present in the coordination sphere of either complex but also the equilibrium constant between the two is of an order of magnitude which allows concentration of both to be measured readily by spectrophoto-metric methods. This allows the effect of the dielectric constant of the solvent on the ratio of the species to be studied easily without the perturbing effect of specific interactions caused by differences in the tendency of the solvents to enter the coordination sphere. 

The acidity function does not and cannot fully account for effects of specific interactions (Section 4-3) between solute and solvent except as they reflect the behavior of the nitroanilines. The quantity Hq therefore should be used as permissive rather than conclusive evidence for mechanisms of reactions or even for relative acidities. 

EFFECT OF SPECIFIC INTERACTION ON MISCIBILITY WINDOWS OF PVC/SAN S COPOLYMER BLENDS... 

Cowie, J.M.G., Devlin, B.G., McEwen, I.J. Surface enrichment in PS/PVME blends 2. The effect of specific interactions in the bulk mixture. Polymer 34, 4130-4135 (1993)... 

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